1. Field of the Invention
The present invention relates to a gas phase growth system, such as a CVD system, in which an organometallic complex vaporized by means of a vaporizer is fed into a reaction chamber to form a film on a substrate in the reaction chamber, and also relates to a method of operating the system, and a vaporizer included in the system. More particularly, the present invention relates to a technique for preventing undesirable deposition of products, which are formed from the organometallic complex, onto a surface of parts of the system, such as the vaporizer and lines connected thereto.
2. Description of the Related Art
In a ULSI, particularly a logic circuit, aluminum (Al) has been used as a wiring material. However, problems of increasing in wire delay-time and wiring fault caused by high electric resistance and poor electromigration resistance of Al often arise, due to the recently high degree of integration of the circuit. Thus, copper (Cu), having a low electric resistance and an excellent electromigration resistance, has been recently used as the wiring material.
Copper wiring is carried out by a process called damascine in which an inter-layer insulating film is etched to form grooves and holes according to a predetermined wiring pattern, copper is deposited in the grooves and holes, and then unnecessary parts of the copper is ground away. At present, a copper film is deposited mainly by the PVD method to form a seed film, and by the electroplating method to form wiring.
However, due to the recent refinement of devices, the aforementioned methods are no longer sufficient for keeping up with current standards involving the seed film formation and the wiring. As a result, a CVD (chemical vapor deposition) method, which enables a satisfactory coverage, has recently been the focus of attention as a next generation seed film forming and wiring art.
When forming a copper film by the CVD method, it is necessary to feed gas including copper into the reaction chamber. However, in general an inorganic compound of copper has a low vapor pressure, so very high temperature and high vacuum are required in order to convert it to a gas state. Under these circumstances, recently, in the film forming process, an organometallic complex of copper, such as hexafluoroacetylacetonate trimethyl vinylsilane copper (hereinafter, referred to as Cu (hfac) TMVS), which has a high vapor pressure, has been used as a raw material. The organometallic complex is a molecule (an ion) containing an organic matter and a metal, and formed by coordinate bonding of organic molecules (ions) to metallic atoms.
The organometallic complex is generally in a liquid state or a solid state under normal temperature and pressure. Therefore, in the film forming process, an organometallic complex is vaporized by a vaporizer, and then fed into the reaction chamber.
However, the organometallic complex is generally unstable. This is because bond energy of the coordinate bond between metallic atoms and organic molecules is smaller than bond energy between molecules, in general. Therefore, under a certain unbalanced condition, the organometallic complex gradually decomposes. While the vaporized organometallic complex is traveling to the reaction chamber, products formed from organometallic complex are inevitably deposited on inner walls of the vaporizing chamber of the vaporizer and inner surfaces of pipes connecting the vaporizer to the reaction chamber. Accretion of such deposits causes reduction in the cross-sectional area of the pipes and results in clogging, thus periodical removal of these deposites is necessary.
Japanese Patent Laid-Open Publication Hei10-88349 discloses a method of removing such deposits. In this method, a cleaning liquid of trimethyl vinylsilane (TMVS) is fed into a pipe, which connects a reservoir of organometallic complex (liquid) and a vaporizer. The cleaning liquid is fed into the vaporizer, a pipe connecting the vaporizer and a reaction chamber, and the reaction chamber, in that order, thus removing deposits in each area.
Japanese Patent Laid-Open Publication Hei08-176826 discloses a CVD system. In this system, a solvent in a liquid state acting as a cleaning liquid is always fed into a vaporizer together with inert gas. When the film forming process is carried out, an organometallic complex in a liquid state is fed into the vaporizer together with the solvent.
However, when the solvent is fed into the pipe for the organometallic complex as in the case of the former (Japanese Patent Laid-Open Publication Hei10-88349), a considerable amount of time is required to remove the cleaning liquid, resulting in reduction in the operation efficiency of the system. Even if a lot of time is spent on removal, it is difficult to remove the cleaning liquid completely, and some cleaning liquid may remain in the system. If this is the case, concentration of the raw material fed into the vaporizer is inconsistent, and thus a problem arises in that the replication of the process is adversely affected. Further, since the vaporizer is cleaned with a liquid, the temperature of the vaporizer lowers and a considerable time is required to return the vaporizer to its original temperature. During this period of time, the next process cannot be performed, thus resulting in a reduction in the operation efficiency of the system. In addition, the temperature of the vaporizer becomes unstable, thus the replication of the process is adversely affected. Also, when a liquid is used for cleaning, a large amount of cleaning liquid is required, which it is not economically desirable.
Also, in the case of the latter (Japanese Patent Laid-Open Publication Hei8-176826), the concentration of the raw material to be sent to the vaporizer inevitably becomes inconsistent.